Answer Happy

a) Consider the set of suspension insulators shown in Figure Q4 below. The capacitance between each pin and earth is 2/10 of the self-capacitance of the unit, while the capacitance from each pin to the guard ring is 2.5/10 of the self-capacitance of the unit. i) Apply Kirchhoff's current laws at nodes P and Q to derive the corresponding voltage equations [4 marks] ii) Determine the voltage across each disc of suspension insulators as a percentage of the 33 kV phase to earth voltage [9 marks) iii) Calculate the string efficiency [2 marks] b) Assume the guard ring is removed. Determine: 1) the voltage across each disc of suspension insulators as a percentage of the 33 kV phase to earth voltage [5 marks] ii) the string efficiency [2 marks] c) Using your answers from parts a) and b) above, explain why guard rings are used on a string of insulators. [3 marks) 1. с mc HH . < La P 1. C + mc HH O وله Іь Iz C Figure Q4 [Total: 25 marks